A magnitude 3.6 earthquake broke at 11:42 p.m. Wednesday beneath the sea floor 16 miles west-northwest of San Clemente Island, the US Geological Survey says. The quake, which was not widely felt on the mainland, appears to have occurred on an unnamed fault southeast of the Santa Cruz fault system. The quake broke near the surface of the sea floor, and it comes just over one day after a 4.0 quake broke beneath the sea floor far off the coast of Malibu.